Contents indicates data such as video data and music data that is stored in electronic files. Examples of contents distribution forms include the client-server type and the “peer to peer” type (hereinafter referred to as “P2P”). In a client-server type system, a request for contents is issued from a client to a server that distributes contents, and a file storing the contents is delivered from the server to the client.
In a P2P system, on the other hand, each of node devices called peers connected to a network serves as both a client and a server. In a contents distribution system of the P2P type, contents requesting peers exchange files directly with peers that hold files including the contents.
When contents is downloaded in a P2P distribution system, the target file is identified with the use of the metadata describing the file name or title of the contents or the identifier of the file. The target file is then downloaded from a peer that holds the file.
An example of a technique involving contents is disclosed in Patent Literature 1 which will described later. This literature discloses a technique for determining whether retrieved media contents correspond to the identifier designated by a user with respect to desired contents.